The present invention relates to a system for controlling and/or regulating the driving response of a motor vehicle having at least two wheels, the system including: at least one sensor device, which detects wheel speeds of at least two wheels, and a data processing device, which determines at least one motion relationship of at least two wheels relative to one another according to the wheel speeds detected.
In addition, the present invention relates to a method of controlling and/or regulating the driving response of a motor vehicle having at least two wheels, implemented for example by the system according to the present invention, the method including the following steps: detecting wheel speeds of at least two wheels, and determining at least one motion relationship of at least two wheels according to the wheel speeds detected.
Conventional systems, such as TCS, ABS, and ESP, may regulate the driving response of a motor vehicle. As a rule, these systems intervene in the operating state of the vehicle on the basis of slip, i.e., the instantaneous wheel slip is monitored by sensors and kept in a favorable range by changing a driving torque which is output by the engine and/or by changing wheel brake pressures. As a rule, this range is one in which the greatest possible coefficient of friction between the wheel and the driving surface may be utilized.
In contrast to straight-ahead driving, errors may be made in establishing the actual wheel slip occurring during cornering due to differing wheel velocities of the individual vehicle wheels.
An error of this type occurs because an Ackermann condition is maintained in axle pivot steering. The Ackermann condition defines the position of the individual wheels of a motor vehicle during travel through curves and requires that the extended rotational axes of all wheels of a motor vehicle intersect in one point. This point is then the instantaneous pole around which the vehicle rotates. Since the rear wheels of a motor vehicle are, as a rule, not steerable, the instantaneous pole may be on an extension of the rotational axis of the rear wheels, which are arranged essentially coaxially. All wheels of the vehicle then have a different distance from the instantaneous pole and therefore have different wheel speeds and/or wheel velocities during travel through curves, from which devices which determine the wheel slip with reference to a comparison of wheel speeds of different wheels establish an apparent wheel slip without it actually existing.
In vehicles having front-wheel drive, too high a slip, i.e., positive slip, is recognized due to the geometrical slip, while in vehicles having rear-wheel drive, too low a slip, i.e., trailing slip, is recognized.
The present invention may be refined in relation to the above-described conventional systems in that the data processing device may establish at least one cornering motion variable of the vehicle according to at least one motion relationship determined.
This example embodiment of a system according to the present invention may allow precise establishment of the at least one cornering motion variable using low outlay for sensors. In this case, only wheel speeds are detected and the establishment of the at least one cornering motion variable is thus based on the actual conditions prevailing between the driving surface and the wheels. Using the present invention, methods for control and/or regulation of the driving response of the vehicle may be performed, for example, on the basis of the established cornering motion variable with greater precision than before.
A suitable motion relationship may be, for example, a speed differential between two wheels, such as between two wheels arranged at a distance from one another in the transverse vehicle direction, e.g. between two front wheels and/or between two rear wheels. From this speed differential it may be directly derived that the vehicle is cornering. In this case, the speed differential of the steered wheels in the steered state may be different from the speed differential of the unsteered wheels. Due to the proportionality between wheel speed and translational wheel velocity, the statements made above and in the following apply both for speeds and for translational wheel velocities, i.e., for the velocity of a wheel center point.
A yaw rate and/or a curve radius and/or a transverse acceleration and/or a geometrical slip of the vehicle may be established from such a speed differential as a cornering motion variable. The apparent slip described above which arises due to the Ackermann condition being observed is referred to as geometric slip.
To establish the speed differential between two wheels, according to an example embodiment of a system of the present invention, at least two wheels lying opposite one another in the transverse vehicle direction may each be assigned a sensor device. Additionally, for example, at least two wheels arranged one behind the other in the longitudinal vehicle direction, or every wheel of the vehicle, may likewise be assigned a sensor device. The more wheels assigned a sensor device of this type, the more precisely the at least one cornering motion variable may be established.
A tire sensor device and/or a wheel bearing sensor device may be considered as a suitable sensor device. These sensor devices may detect wheel speeds directly on the wheel and, in addition, are capable of detecting additional information about forces acting between wheel and driving surface. Of course, the wheel speed may be detected using a conventional speed sensor, such as one including a pulse ring and a sensor, such as that used in antilock braking systems. The present invention, by contrast, may require only one single type of sensor, namely a sensor detecting the wheel speed.
In order to be able to make the detected and/or established values available for processing, an example embodiment of system may include a memory device. Selected vehicle geometry data may be stored in this memory device, with reference to which, together with the wheel speeds detected, the at least one cornering motion variable may be established.
According to one example embodiment of the present invention, the data processing device may, according to the at least one cornering motion variable established, perform a correction of a motion variable, for example the vehicle velocity or a wheel slip, which is calculated from the wheel speeds detected.
In addition, the data processing device may output an actuating signal to enhance the traffic safety according to the cornering motion variable established, the example embodiment of the system further including an actuator which influences an operating state of the motor vehicle according to the actuating signal. Subsequently, the vehicle velocity may, for example, be regulated according to the yaw rate and/or the transverse acceleration established.
The number of components required for implementing the example embodiment of the system according to the present invention may be kept low if the data processing device and/or the actuator is/are assigned to a device for controlling and/or regulating the driving response of a motor vehicle, such as a TCS, an antilock braking system, or an ESP system.
The control and/or regulation of the driving response may be improved through a corresponding device in that the device for controlling and/or regulating the driving response of a motor vehicle selects control and/or regulation algorithms as a function of the at least one cornering motion variable established.
In one case, for example, the actuator may be assigned to a TCS and/or be part of a TCS which switches between traction-prioritized and driving stability-prioritized regulation as a function of the curve radius established, taking the vehicle velocity into consideration, for example. Therefore, for example, for small curve radii, regulation may be performed in such a manner that the highest possible traction is achieved, while for greater curve radiixe2x80x94and possibly at higher vehicle velocitiesxe2x80x94high driving stability is given priority.
In other words, the features of the present invention may be achieved through a system for controlling and/or regulating the driving response of a motor vehicle having at least one wheel, the geometrical slip and/or the curve radius and/or the yaw rate of the vehicle being established from the wheel motion behavior detected.
The present invention may also include a step of establishing at least one cornering motion variable of the vehicle according to the motion relationship determined. Using an example method according to the present invention, the features cited above in connection with an example embodiment of the system according to the present invention may also be achieved, for which reason reference is expressly made to the description of the system according to the present invention for supplementary explanation of the example method.
As previously explained, to establish the at least one cornering motion variable a speed differential between two wheels is determined as a motion relationship. This may be a speed differential between two wheels arranged at a distance from one another in the transverse vehicle direction, such as, for example, between the front wheels and/or between the rear wheels.
The at least one cornering motion variable may be precisely established if the wheel speed of as many vehicle wheels as possible is detected, such as, for example, all of them.
A yaw rate of the vehicle may be calculated particularly easily as a cornering motion variable from a speed differential between two wheels arranged at a distance from one another in the transverse vehicle direction. For this purpose, only knowledge about the geometrical ratios of the vehicle may be additionally required. This information may be stored in a memory device. Furthermore, a curve radius may be established as a cornering motion variable with the aid of the yaw rate. To establish the curve radius, it may be, for example, sufficient to know an average velocity of non-driven wheels and the yaw rate, since the average velocity of non-driven wheels may be calculated from corresponding wheel speeds of these wheels through averaging. In some circumstances, the curve radius may be established directly from the speeds of the vehicle wheels while taking the Ackermann condition or the track width into consideration is also conceivable. A transverse acceleration of the vehicle may also be established as a cornering motion variable from the average velocity of non-driven wheels and the yaw rate.
In addition, as previously described in connection with an example embodiment of the system according to the present invention, the geometrical slip of the vehicle produced by observing the Ackerman condition during cornering may be established as a cornering motion variable. If this apparent slip is known, variables derived from the wheel speeds, such as vehicle velocity and wheel slip, may be corrected appropriately and determined more precisely. Furthermore, the established geometrical wheel slip of the wheels on the inside of the curve may be taken into consideration for the slip threshold calculation of slip-based control and/or regulation devices and the precision of the control and/or regulation may be enhanced in this manner. These types of devices may be, for example, antilock braking systems, TCS, and/or ESP systems.
The geometrical slip of the wheels on the outside of the curve may be used as a gauge for the possible lateral traction of the vehicle during cornering and, in addition, may be taken into consideration for an SDOC determination. The abbreviation SDOC stands for xe2x80x9csystem deviation outside curvexe2x80x9d in this case.
More extensive information on the precise establishment of the cornering motion variables cited is given further below in connection with the description of the figures.